For a micromachining or processing such as, for example, etching, deposition, oxidation, or sputtering in a manufacturing process of a semiconductor device or a flat panel display (FPD), plasma is used to subject processing gas to an excellent reaction at a relatively low temperature. Discharge is typically used for generating plasma. Plasma processing apparatuses are generally classified into a plasma processing apparatus using high-frequency discharge and a plasma processing apparatus using microwave discharge. High-frequency discharge systems are also classified into a capacitively coupled system in which a parallel flat panel electrode is provided within a processing container and an inductively coupled system in which a spiral or swirling electrode is attached around the processing container. Among several plasma generation systems, the capacitively coupled system has become a mainstream of a device for mass production and a device for device development.
In the capacitively coupled plasma processing apparatus, an upper electrode and a lower electrode are arranged in parallel within a pressure-reducible processing container or reaction container, a processing target substrate, for example, a semiconductor wafer, is placed on the lower electrode, and high-frequency waves having a predetermined frequency are applied to the upper electrode or the lower electrode through a matching unit. Electrons are accelerated by a high-frequency electric field generated by the high-frequency waves, plasma is generated by dissociation and ionizing collision of the electrons with molecules and atoms of the processing gas, and a desired plasma processing (for example, an etching process) is performed on a wafer surface by radicals or ions in the plasma.
In a plasma process, (in-plane) uniformity of the process is a basic requirement for improving yield, the importance of the (in-plane) uniformity gradually increases with the progress of miniaturization of the semiconductor device or an increase in diameter of the semiconductor wafer, and a required level thereof increases. In this regard, in a conventional capacitively coupled plasma processing apparatus, the uniformity of the process significantly depends on uniformity of the density of plasma on the semiconductor wafer. Thus, researches have been conducted into a structure of an electrode used for generating plasma, in particular, an electrode (high-frequency electrode) to which the high-frequency waves are applied.
As one typical example, a capacitively coupled plasma processing apparatus is known, in which an upper electrode facing a lower electrode on which a substrate is placed is divided into an inner electrode and an outer electrode in a radial direction to variably control a ratio of high-frequency powers for generating plasma which are distributed to both electrodes (Patent Document 1).
In the capacitively coupled plasma processing apparatus, the outer upper electrode is electrically connected to an output terminal of a high-frequency power supply that outputs the high-frequency waves for generating plasma through a cylindrical conductive member and the inner upper electrode is electrically connected to the output terminal through a rod-shaped central conductive member. A variable condenser is inserted in the middle of the central conductive member, so that capacitance of the variable condenser is variably controlled by, for example, a step motor.
In this case, as the capacitance of the variable condenser is increased, a ratio (outer/inner power distribution ratio) (Po/Pi) of a power (Po) distributed and supplied to the outer upper electrode (that is, powers introduced into plasma through the outer upper electrode) and a power (Pi) distributed and supplied to the inner upper electrode (that is, powers introduced into plasma though the inner upper electrode) is decreased. Conversely, as the capacitance of the variable condenser is decreased, the ratio (outer/inner power distribution ratio) (Po/Pi) is increased. As a result, the capacitance of the variable condenser may be variably controlled such that a plasma density distribution or a profile of a process characteristic in the radial direction is controlled in the chamber.